Seat belt tension sensor, methods of integration and attachment

ABSTRACT

A force sensor ( 50;50′;50   a ) for generating a signal indicative of the usage of a seat belt comprising:  
     a cylindrical first housing ( 70;70′ ) having a wall ( 72 ) and a bottom ( 74 ), the bottom including an opening ( 76 ), the first housing including an internal cavity ( 124 );  
     a cable anchor ( 90 ) slidably received within the cavity and adapted to be connected to a cable ( 54 );  
     the cable ( 54 ) having one end secured to the cable anchor and another end operatively connected to an anchor point;  
     a magnet ( 120 ) operatively connected to a top of the cable anchor and movable with the cable anchor;  
     first means for biasing the cable anchor to resist motion of the cable anchor toward the bottom of the housing;  
     a magnetic sensor ( 200 ) for generating a signal indicative of the distance between it and the magnet;  
     a sensor housing ( 180 ) securably connected relative to the first housing and positioned upon the first housing to position the magnetic sensor a determinable distance from the magnet at a null position;  
     a housing end cap ( 150 ) securable to the first housing for enclosing an open end of the first housing, the magnet and the magnetic sensor being relatively movable when a force of a determinable level is applied to the end cap thereby causing the relative movement of the magnet and the magnetic sensor.

[0001] This is a regularly filed utility patent application claimingpriority of provisional patent application 60/202,162, filed May 4,2000.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The invention generally relates to safety restraint systems andmore particularly to a sensor that is capable of measuring a force ortension in a component of a seat belt system, generally between theanchor point and the seat belt buckle.

[0003] In order to comply with government-mandated and market-driveninjury reduction measures relating to the undesirable deployment ofvehicle safety restraints in general and air bag restraint systems inparticular, it is often desirable to determine the weight of theoccupant in the front passenger seat. The weight of the front seatoccupant is an important criterion to determine their ability towithstand an air bag deployment and is also a variable that can be usedin setting which level of a multi-level air bag inflator should be used.Seat-based weight sensors have been developed to measure the occupant'sweight. However, these weight sensors suffer from a deficiency relatedto the imposition of additional force in a downward direction onto theseat that can be imparted by a cinched or tightly fitting seat belt.This deficiency is particularly problematic with a belt tightlyenveloping a child restraint (such as a child seat) into the vehicleseat. In view of this added downward force the control system mightmistakenly conclude that a small adult or large child is seated on theseat instead of a child seat causing an incorrect deployment decision tobe made as the weight sensor only measures the total downward force onthe seat.

[0004] A force (or tension) sensor with the ability of sensing thetension (force) in the belt system can be used to more accuratelydifferentiate the type or size of occupant, child seat, etc. in thevehicle seat. Additionally, such a force or tension sensing mechanismcan also be used, not as a supplement to determine occupant weight butas an indication that the seat belt is properly tightened about theoccupant or, alternatively, tightened about a child safety seat.

[0005] The present invention allows the incorporation of a smalldisplacement controlled by a spring force between the belt system and ananchor point. The measurement of the displacement change due to tensionin the belt system is sensed by magnetic sensor or other means, thusproviding a signal indicating the tension in the belt system.

[0006] The sensor further provides a separate load path, via a stop, sothat the maximum belt load achieved during a crash event can be safelycontained.

[0007] It is an object of the present invention to provide a seat belttension or force sensor.

[0008] Accordingly the invention comprises a force sensor for generatinga signal indicative of the usage of a seat belt comprising: acylindrical first housing having a wall and a bottom, the bottomincluding an opening, the first housing including an internal cavity; acable anchor slidably received within the cavity and adapted to beconnected to a cable (54); the cable having one end secured to the cableanchor and another end operatively connected to an anchor point; amagnet operatively connected to a top of the cable anchor and movablewith the cable anchor; first means for biasing the cable anchor toresist motion of the cable anchor toward the bottom of the housing; amagnetic sensor means for generating a signal indicative of the distancebetween it and a magnet; a sensor housing securably connected relativeto the first housing and positioned upon the first housing to positionthe sensor means a determinable distance from the magnet at a nullposition; a housing end cap securable to the first housing for enclosingan open end of the first housing, the magnet and the sensor means beingrelatively movable when a force of a determinable level is applied tothe end cap, thereby causing the relative movement of the magnet and thesensor means. Various other embodiments are shown.

[0009] Many other objects and purposes of the invention will be clearfrom the following detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the drawings:

[0011]FIG. 1 shows a rudimentary three-point seat belt system.

[0012]FIG. 2 is an assembly view showing many of the major components ofthe first embodiment of the invention.

[0013]FIG. 3 is a cross-sectional view of a sensor through section 3-3of FIG. 7. The force sensor is in a null or unforced condition.

[0014]FIG. 3a shows the force sensor in a loaded condition.

[0015]FIG. 3b is a partial cross-sectional view of a sensor housing alsoshown in FIG. 3.

[0016]FIG. 4 is an isometric view of a magnet retainer.

[0017]FIG. 4a is a cross-sectional view through section 4 a-4 a of FIG.4.

[0018]FIG. 5 is an isometric view showing the magnet retainer secured ona cable anchor.

[0019]FIG. 6 is a cross-sectional view through section 6-6 of FIG. 3.

[0020]FIG. 7 is a cross-sectional view through section 7-7 of FIG. 3.

[0021]FIG. 8a illustrates an alternate embodiment of a force sensorhaving a cylindrical profile.

[0022]FIG. 8b shows a step in the assembly of the embodiment of FIG. 8.

[0023]FIG. 8c shows an alternate cylindrically shaped force sensor.

[0024]FIG. 9 is an assembly view showing a further alternate embodimentof the invention.

[0025]FIG. 10 shows an assembled sensor in a null condition.

[0026]FIG. 11 shows the sensor in a force deflected, force sensingcondition.

[0027]FIG. 12 shows another embodiment of a sensor retainer.

[0028]FIG. 13 shows a further embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] Reference is briefly made to FIG. 1, which illustrates athree-point safety system 20 comprising a seat belt 22 divided into ashoulder belt portion 24 and lap belt portion 26. The shoulder belt isthreaded through a D-ring 28 and received and rewound upon a spool of aretractor 30. The retractor is appropriately anchored as shown generallyby numeral 32. The anchor can be the floor, the frame or the vehicleseat. The transition between the shoulder belt and the lap belt isdefined by a tongue 34, which is inserted within a buckle 36. The buckleis secured to an anchor point 40, which would be the vehicle floor,vehicle frame, or vehicle seat. The end of the lap belt opposite thetongue is similarly anchored. FIG. 1 also shows a tension or forcesensor of the present invention 50. The sensor 50 is attached eitherdirectly to an anchor point 40 or, for example, to the anchor pointthrough a pretensioner (also referred to as a belt tightener) 52 througha cable 54. Depending upon the typical installation and design of thebelt tightener, the cable 54 may be routed about a pulley 56. As isknown in the art, the pretensioner will include a tubular housing inwhich one end of the cable is secured to a piston. As the piston isdriven down the tubular housing by a selectively excitable charge ofpropellant, slack in the seat belt about the seated occupant is removed.As mentioned above, the pretensioner is an optional feature of thepresent invention.

[0030] With reference to FIGS. 2 and 3, it can be seen that the majorelements of the present invention comprise a cylindrically shapedhousing 70 having a cylindrical wall 72 and a bottom 74. The bottom 74includes an opening 76. Inserted within the opening 76 is a bushing 80having a hollow, generally cylindrical body 82 and a flange 84. As canbe seen from FIG. 3, flange 84 sits on bottom 74 with the cylindricalportion 82 extending through the opening 76. As can also be seen moreclearly in FIG. 3, the inner wall of the cylindrical portion 82 isarcuately shaped to provide an annular contact point (see numeral 86) toreduce sliding contact. The interior of the housing 70 defines a cavity88. The bushing, and more particularly the curved portion 86, can beformed integrally as part of the bottom. The sensor 50 further includesa cable anchor 90, which includes a cylindrical body 92, whichterminates at a wider flange 94. The anchor 90 includes a hollow bore 96into which an end 98 of the cable 54 is received and secured such as bycrimping. As can be appreciated, the cable 54 will be secured to theanchor 90 prior to installing the anchor within the sensor 50. Situatedatop the anchor 90 is a magnet retainer 100. In the embodimentillustrated, the retainer 100 is a plastic part having a cylindricalbody 102 with three flexible depending legs 104. Each of the legs 104includes a clip fastener 106 to enable the retainer 100 to be snap fitabout top of the cable anchor 90 (see FIGS. 3 and 5).

[0031] As can be seen in FIGS. 4 and 4a, the magnet retainer includes acenter hub 108 having a bore 110 and plurality of webs 110 securing thehub to the outer wall of the body 102. A magnet 120 is not shown in FIG.4 but is shown in FIG. 4a and is secured to the retainer 100 at the bore110. As can be seen in FIG. 3, the retainer 100 includes a web 122 atthe bottom of bore 110 to provide a platform upon which the magnet canbe properly fastened. The top 102 b of the side wall 102 a extends abovethe web 108 and the top of the magnet 122 and acts as a stop and definesa gap, g, with mating parts and also assists in setting the preloadforce of a bias spring. It should be appreciated that the retainer 100properly locates the magnet relative to the end of the cable anchor 90,however, the magnet retainer can be integrally formed as part of end 124of the anchor, such as by cold-forming a projecting boss, which wouldprovide a platform that is similar in function to the web 122.Additionally, the anchor 90 can be formed with a recess (see the phantomline 126) into which the magnet can be placed. As can be appreciated, ifthe magnet retainer 100 is integrally formed at the end of the cableanchor 90, the length of the end 124 of the cable anchor would beappropriately lengthened (or the spring can be moved upwards making thesensor 50 smaller and lighter as well as eliminating two parts) suchthat the magnet is positioned at the location shown in FIG. 3.

[0032] The sensor 50 additionally includes a cylindrical piston 140. Thepiston 140 includes a step bore 142, which defines the preferredthickness of the walls of the piston. The piston 140 radially stabilizesthe cable anchor relative to the longitudinal axis of the sensor 50 andprevents the anchor 90 from cocking, which would add friction and alsoimproperly move the magnet relative to a magnetic sensor. As can beseen, the upper cylindrical wall 144 a envelops the sides of the flange94 to further stabilize the anchor. An intermediate wall 144 b providesa step below the underside of the flange and reduces the size of thebore 142 such that it is closely spaced relative to the body 92 of thecable anchor 90 providing added support. The lower wall 144 c is of thelargest diameter and defines a spring-receiving cavity 146 for acompression spring 148. As can be seen, when the cable anchor 90 ispulled relatively downwardly by the cable 54, the spring 148 resiststhis motion and urges the piston 140 and hence the cable anchor 90upwardly. As can be appreciated, the bottom 145 of the piston will actas a stop if the force sensor 50 (50′) is subjected to very highseparating forces such as may occur during the operation of thepretensioner 52.

[0033] The sensor 50 additionally includes a cap (or buckle anchor) 150that is secured to the housing 70. As can be seen, the cap 150 is hollowand has threads 152, which mate with threads 154 formed on the housing70. As can be appreciated, various other methods of attachment can besubstituted. The cap 150 functions as a buckle anchor and includes afastener or anchor 154 that is adapted to be secured, either directly orindirectly, such as through a cable (see phantom line 156 in FIG. 2), ora length of seat belt webbing to the buckle 36 or a rivet (not shown).

[0034] With reference to FIG. 3, it can be seen that the walls 160 ofthe cap also define a cavity 162. Fixedly positioned relative to the capis a sensor retainer 180. FIG. 3b shows a partial cross-sectional viewof the sensor retainer. The sensor retainer has a cylindrical body 182with a cylindrical flange or sleeve 184 that is received within acylindrical groove 186 formed on an interior wall of the cap 150. Thesleeve or flange 184, on an interior wall, includes a circularprojection 185, which is preferably semi-circular in cross-section toradially stabilize the piston relative to the axis of the sensor 50. Theshape of the projection 185 provides for a point contact, furtherreducing friction. The projection can also be flat but preferably of ashort dimension to keep friction low. In the illustrated embodiment thesensor retainer is sandwiched between the housing 70 and the cap 150.The top 188 of the sensor retainer includes a groove, passage, or bore190 into which a magnetic sensor 200 is received. The magnetic sensorcan be, for example, a Hall effect or variable reluctance sensor, or amagneto-restrictive sensor which provides a signal, the level of whichvaries in relationship to the relative distance between it (the magneticsensor) and the magnet 120. Wires, such as 202, emanating from thesensor 200 can be communicated out from the force sensor 50 through anopening 204 in the cap. The wires are communicated to conditioningelectronics or directly to a microprocessor. Sensors of the varietymentioned above can provide a variable signal indicative of the variabledistance between the magnet 120 and the sensor or, alternatively,provide a digital output (on or off) indicative that a certainseparation distance has been achieved as the force sensor 50 is loaded.

[0035] Reference is again made to FIG. 1, as well as FIG. 3a. As can beappreciated, when the tongue is latched into the buckle and when the lapbelt is drawn tightly about the occupant, the tongue 34 will pullupwardly on the buckle. This action also urges the occupant onto theseat or urges a child seat 35 (see FIG. 1). As mentioned above (see FIG.2), the buckle 36 is secured to the force sensor 50. This upward force(see arrow Fl) will tend to move the force sensor 50 upwardly againstthe bias force of the spring. The reaction force acting through theanchor is shown by arrows F2. The applied forces will cause the springto compress and, as such, move the magnet ever so slightly away (seeFIG. 3a) from its rest position (shown in FIG. 3) relative to the magnetsensor 200. A sensor output differing from that which is generated atthe rest position would indicate that the lap belt has been properlysecured about the occupant and also indicate a measure of the downwardforce the seat belt system is applying to the seated occupant orbuckled-up child seat.

[0036] Reference is briefly made to FIGS. 8a and 8 b as well as to FIGS.2 and 3. FIGS. 8a and 8 b show an alternate force sensor 50′, whichutilizes many of the components previously described in relationship toFIGS. 2 and 3. As can be seen, the housing 70′ of this force sensor isconsiderably longer than the housing 70 of FIG. 2. Additionally, thethreaded connection between housing 70 and connector 150 has beenremoved. In this embodiment, the housing 70′ includes a plurality ofopenings 300 disposed about its periphery near an upper end thereof. Thewalls 302 of the cap 150 include a plurality of engagement features 304,such as a triangularly shaped projection. The cap 150 is pushed withinhousing 70′ such that the features 304 are received and locked withinopenings 300. Thereafter, end 306 of the housing 70′ is bent or swagedover (see arrow 307) to retain the cap 150 in place. FIG. 8a also showsa similar variant with regard to how to secure the sensor retainer 150in place. The sensor retainer 180′ of FIG. 8a also includes a pluralityof projections 310, each of which is received within a correspondingopening 312, also formed within the wall of housing 70′.

[0037] As mentioned earlier, the cable retainer can include provision tohold and retain the magnet 120. The cable retainer 90″ includes a bore110 to receive the magnet. Additionally, the top of the cable retainer90″ is formed in the shape of the top of the magnet retainer andincludes an integrally formed, preferably annular wall 102 a, whichspaces the magnet properly relative to the sensor retainer 180″. As canbe seen, the housing 70″ and the sensor retainer 180″ do not include theopenings 312 and projections 310 shown in FIG. 8a, which were used tohold the sensor retainer in place in the housing 70′. Instead, housing70″ is formed with an annular groove 320, which receives thecomplementary-shaped lower surface 322 of the cylindrical flange orsleeve 184. As can be appreciated, when the top of the housing 70″ isbent over, it retains both the buckle retainer 50″ and the sensorretainer 180. If this bent-over method of securing is sufficient, theprojections 304 and openings 300 can be removed. The above-mentionedpiston 140 is not used in this embodiment. As can be seen, the flange94′ of the cable retainer slides against the circular projection 185(formed in an annulus). The housing 70′, further includes an annulargroove 324 with a cylindrical side wall 324 and an inner wall 328, whichis angled upwardly to give the groove a sharp notch or V-like shape. Thelower surface 340 includes an angled, peripheral wall 342 that is shapedto matingly engage with the inner wall 328. When the spring 148 iscompressed and the wall 328 engages wall 342, the reaction forces aredirected inwardly, which prevents the housing from buckling. As can beappreciated, the part count of this embodiment has been lowered, whichshould result in a lower cost and with the removal of the piston, thediameter of the sensor 50″ can be made smaller than the earlierembodiments.

[0038] Reference is made to FIGS. 9-11, which show a further embodimentof a force sensor 50 a. FIG. 10 shows the null position of the sensorand FIG. 11 shows the active state of the sensor with the magnet moved adistance, d, relative to the stationary sensor. The force sensor 50 aincludes a housing 70 a having two parts 71 a and 71 b, which clamptogether or fit together in a clam shell manner. Each of the housingparts 70 a and 70 b is preferably formed as a metal stamping, forging orcasting. The housings include two upraised bridge portions 400 and 402.As can be appreciated, when the housing parts are mated together, theopposed bridge sections 400 and 402 provide a passageway for variousmoveable parts. Each of the housing portions includes a plurality ofopenings 404, which can be secured together by rivets 406 or otherfastening mechanisms including welding. An end 55 of cable 54 is securedto a cable retainer 90 a. As can be seen, the cable retainer is formedas a square annulus. The bottom 410 of the retainer is wider than thediameter of the cable 54. Portions 412 a and 412 b, which extendoutwardly from the cable, function as a stop (as described below). Themagnet 120 is received within a magnet retainer 100 a, which includesflexible legs 104, which are clipped about the top or far end 414 of thecable retainer.

[0039] This force sensor 50 a also includes a sensor retainer 180 a intowhich a magnetic sensor 200 is received. As can be seen from FIG. 9, thesensor retainer 180 includes a plurality of integrally formed bosses419, which are received within openings 422 formed in each of thebridges 402 (of the housing parts 71 a and 71 b). The cable 54 isreceived within a hollow sleeve, which functions as a bushing 86 a. Thebushing or sleeve 86 a includes a flange 420. When in position, theflange 420 rests against the flange or stops 412 a and 412 b of thecable retainer. A spring 148 is fit about the bushing 86 a and biasesthe cable anchor 90 a into the housing 70 a and resists the outwardpulling motion of the cable 54.

[0040] Reference is again made to the housing parts 71 a and 71 b. Eachhousing part includes a pair of steps 430, which are sized to receivethe extending portions 412 a and 412 b of the anchor 90 a and, incombination with these portions, act as a stop (see FIG. 9) to preventexcessive outward motion of the cable. It should be noted that topbridge 400 in FIGS. 10 and 11 has been removed to show opposing walls440, which guide the cable retainer 90 a as it slides back and forth.The sensor retainer and sensor are also shown in cross-section in thesefigures.

[0041]FIG. 12 shows a further embodiment of the sensor retainer 180 a.In this embodiment the sensor retainer includes a pair of opposing wings442. Each wing 442 includes a crosspiece 444, which extendsperpendicularly relative to the wing 442. Each crosspiece 444 liesadjacent a corresponding side of the cable retainer 90 a and provides alow friction interface with walls 440 of the frame. The crosspieces 442are made of a material that is dissimilar to the frame. In theillustrated embodiment, the entire sensor retainer, including thecrosspieces, is preferably plastic.

[0042]FIG. 13 shows still another variant of the invention and is verysimilar to the embodiment of FIG. 9. In this embodiment, the cableretainer 90 a includes two notches 450 at its far end 414. The magnetretainer 100 b is received against end 414 as in the earlier embodiment,however, retainer 100 b includes a pair of lower wings 452, which arepositioned on the undersurface of the sides of the cable retainer and apair of upper wings 452 rest on the top surface of the cable retainer.The magnet retainer 100 b is further secured to the cable retainer 90 awith depending legs 256, which snap into a corresponding notch 250. Thelegs slide against the frame walls 440 to provide a low-frictioninterface. The legs 256, in combination with the sleeve or bushing 86 a,provide a three-point mounting to prevent the cable retainer fromcocking as it moves.

[0043] Many changes and modifications in the above-described embodimentof the invention can, of course, be carried out without departing fromthe scope thereof. Accordingly, that scope is intended to be limitedonly by the scope of the appended claims.

1. A force sensor (50;50′;50 a) for generating a signal indicative ofthe usage of a seat belt comprising: a cylindrical first housing(70;70′) having a wall (72) and a bottom (74), the bottom including anopening (76), the first housing including an internal cavity (124); acable anchor (90) slidably received within the cavity and adapted to beconnected to a cable (54); the cable (54) having one end secured to thecable anchor and another end operatively connected to an anchor point; amagnet (120) operatively connected to a top of the cable anchor andmovable with the cable anchor; first means for biasing the cable anchorto resist motion of the cable anchor toward the bottom of the housing; amagnetic sensor means (200) for generating a signal indicative of thedistance between it and the magnet, such distance proportional to aforce applied to the seat belt; a sensor housing (180) securablyconnected relative to the first housing and positioned upon the firsthousing to position the sensor means a determinable distance from themagnet at a null position; a housing end cap (150) securable to thefirst housing for enclosing an open end of the first housing, the magnetand the sensor means being relatively movable when a force of adeterminable level is applied to the end cap thereby causing therelative movement of the magnet and the sensor means.
 2. The sensor asdefined in claim 1 wherein the first means includes a hollow,cylindrical piston (140), within the housing cavity (124) and a spring(148) intermediate the piston and the first housing for biasing thepiston and the cable anchor.
 3. The sensor as defined in claim 1 whereina top of the cable anchor includes a flange (94) and wherein the piston(140) includes a mating wall portion (144 a, 144 b) to slidably receivethe cable anchor and to radially stabilize the cable anchor relative toa central axis of the first housing.
 4. The sensor as defined in claim 2further including a low-friction annular guide, cooperable with anexterior wall of the piston to radially stabilize the piston relative toa central axis of the first housing.
 5. The sensor as defined in claim 1including a magnet retainer (100) for holding the magnet to the cableanchor.
 6. The sensor as defined in claim 5 wherein the magnet retainer(100) is non-magnetic.
 7. The sensor as defined in claim 6 wherein themagnet retainer (122) is integrally formed as a part of the cableanchor.
 8. The sensor as defined in claim 4 wherein the annular guide isformed integrally as a part of the sensor housing.
 9. The force sensoras defined in claim 1 wherein the cable anchor and the first housinginclude force means for resisting outward deformation of the firsthousing.
 10. The force sensor as defined in claim 1 wherein the sensorhousing is secured to one of the end cap and the first housing.
 11. Aforce sensor (50 a) for generating a signal indicative of the usage of aseat belt comprising: a first housing (70 a) having first and a secondhousing part, the first and second housing parts each including a firstbridge portion (400) and a second bridge portion (402), the first bridgeportions defining a first passage and the second bridge portionsdefining a second passage; a cable anchor (90) slidably received withinthe first and second passages formed by the bridge portions, the cableanchor adapted to be connected to a cable (54), the cable anchor, at afirst anchor end, includes an annular portion 44; the cable (54) havinga first cable end operatively secured to a second anchor end and asecond cable end operatively connected to an anchor point; a magnet(120) operatively connected to annular portion of the cable anchor andmovable with the cable anchor; first means for biasing the cable anchorto resist motion of the cable anchor toward an end of the first housingopposite the location of the magnet; a sensor housing (180) fixedlypositioned between the second bridge portions and located within thesecond passage, the annular portion of the cable anchor surrounding thesensor housing; a magnetic sensor (200), located within the sensorhousing for generating a signal indicative of the distance between itand the magnet, such distance proportional to a force applied to theseat belt; the magnet and the magnetic sensor being relatively movablewhen a force of a determinable level is applied to the end cap therebycausing the relative movement of the magnet and the sensor means. 12.The sensor as defined in claim 11 wherein at least one housing partincludes a stop for interacting with a part of the of the annularportion of the cable anchor to prevent excess motion of the cableanchor.
 13. The sensor as defined in claim 11 wherein the magnet issupported by a magnet retainer or housing and wherein the magneticretainer is snapped onto the annular portion of the cable retainer. 14.The sensor as defined in claim 11 wherein the sensor housing includes alow friction surface that extends about opposite sides of the annularportion of the cable anchor to reduce friction between the cable anchorand the housing parts.
 15. The sensor as defined in claim 13 wherein themagnet retainer is located on a remote end of the annular portion of thecable anchor and includes wings extending outwardly from opposite sidesof the annular portion to provide a low friction surface between thecable anchor and the housing parts.